PROTON-1442: [C++] Interactive transaction tester

You can interactively declare, commit, abort transactions;
fetch/send messages;
list pending unsettled messages;
release unsettled messages

This needs to be run against a broker that supports transactions

Probably shouldn't be in examples as it's really a tester

This code was written with the assistance of Cursor.

Author: astitcher

cpp/examples/CMakeLists.txt

@@ -61,6 +61,7 @@ foreach(example
     service_bus
     multithreaded_client
     multithreaded_client_flow_control
+    tx_interactive
     tx_send
     tx_recv)
   add_executable(${example} ${example}.cpp)